feature: add custom favicon, fix small typos

src/components/Intro.js

@@ -10,7 +10,7 @@ class Intro extends Component {
         <div className="zen-zone-intro">
           <h1>Welcome to The Zen Zone.</h1>
           <p>A minimalistic meditation area built by <a href="http://tholman.com" target="_blank" rel="noopener noreferrer">Tim Holman</a>, designed to calm you down via the power of small, captivating, mildly amusing and oddly satisfying activities. Feel the Zen!</p>
-          <button onClick={this.props.onButtonClick}>Lets get started</button>
+          <button onClick={this.props.onButtonClick}>Let's get started</button>
         </div>
       </header>
     );

src/components/Reflection.js

@@ -17,7 +17,7 @@ class Reflection extends Component {
           <p>
             You have been meditating with us for <b>{totalMinutes}</b> minutes and <b>{remainingSeconds}</b> seconds.
           </p>
-          <button onClick={this.props.onButtonClick}>Lets do some more?</button>
+          <button onClick={this.props.onButtonClick}>Let's do some more?</button>
         </div>
       </header>
     );